What is a Herbivore?
A herbivore is an animal that gets its energy from eating plants, and only plants. Omnivores can also eat parts of plants, but generally only the fruits and vegetables produced by fruit-bearing plants. Many herbivores have special digestive systems that let them digest all kinds of plants, including grasses.
Herbivores need a lot of energy to stay alive. Many of them, like cows and sheep, eat all day long. There should be a lot of plants in your ecosystem to support your herbivores. If you put carnivores or some omnivores in your ecosystem, they'll eat your herbivores, so make sure you have enough herbivores to support them.